I'm sure we've all noticed the parallels between seasons one and six. Characters in the ALT mirroring their season one selves as well as the 2007 events, of course, but not to mention other more overt and has-to-be intentional similarities with episode centricities: Episodes 1 and 2: multi-centric; episode 3: Kate-centric; episode 4: Locke-centric. A betting man would say the next episode will be Jack-centric. (I don't read spoilers, so I don't mind saying that I'd be a betting man in that situation. :P)
Now the something that really leaped out me during MiB's answer-filled speech to Sawyer in "The Substitute" was his statement that they have three choices:
"It means you have three choices. First, you can do nothing and see how all this plays out. And possibly, your name will get crossed out. Second option. You can accept the job. Become the new Jacob. And protect the island. [...] The third choice, James, is that we just go. We just get the hell off this island. We never look back."
Have we heard the notion of three choices before? Of course, and you know what season that was in.
"You have only three choices: run, hide, or die." -Rousseau
You're saying, "Of course, three choices... but really, big deal." But let's really look at the circumstances.
Take this hypothetical situation: "A mysterious entity approaches a group of people with new found common elements, and tells them that they have to deal with another mysterious entity's threat with one of three choices." Applied:
Rousseau approaches the recently stranded 815 survivors and tells them that the Others are coming and they can either run, hide, or die.
MiB approaches the candidates and tells them that Jacob needs one to replace him and they can either do nothing, accept the job, or escape the island.
If you agree that these situations are quite similar, let's look further at a parallel between the three options:
Run... Escape the island
Hide... Do nothing
Die... Well, the only option left is becoming a new Jacob.
This leads me to the point of this, that two outcomes are implied, if this parallel was intentional. Either one of the remaining candidates (Jack, Hurley, Sayid, Sawyer, or a Kwon) will have to die in order to become Jacob, or it's possible that the real Locke can or will come back in the form of Jacob.
I realize this is a stretch, and don't honestly think we'll ever see a resurrected form of Locke, but I thought it was a cool parallel and thought I'd throw it out there.